The invention relates to a device for producing a multi-component compound, in particular for dental purposes, by mixing its components after they have been pressed out of cartridges which open into a dynamic mixer and are arranged exchangeably in the device, with a first electric motor for advancing all of the pistons assigned to the cartridges, and with a second electric motor for rotary driving of mixing elements in the mixer via a shaft, which is held in engagement with the mixer by spring pretensioning and can be pulled back from the mixer counter to the spring pretensioning.
Multi-component compounds can be dispensed and mixed using a known device of this type (EP 1 279 379 B1). The mixer of said device has to be replaced every so often. This is firstly necessary for hygiene reasons, if the mixed compound remains for too long in the mixer. It is particularly necessary, however, when the mixed compound hardens, since the mixer then becomes unusable after a certain time. In the known device, it is necessary first to pull the pistons back fully for this purpose. At the end of this movement, the shaft driving the mixer is then pulled back and thereby detached from the mixer, which could be done by a cross bracket, for example, that connects the two pistons. The mixer can then be pulled out sideways and replaced by a new one. When the pistons are again moved in order to press the multi-component compounds out, the spring force presses the shaft back into engagement with the mixer.
The disadvantage of this device is that the pistons first have to be fully retracted if the mixer is to be replaced. This does not pose any problems if the cartridges have been completely emptied. In many cases, however, it is desired for the same filling of the cartridges to be partially pressed out a number of times in succession, in which case the mixer has to be replaced if, in the interim, too much time has elapsed between the individual pressing-out operations and the components have therefore at least partially hardened in the mixer. It is in this case disadvantageous if the pistons each have to be fully retracted first of all. This entails a considerable loss of time, particularly in view of the fact that, although the pistons can be retracted quickly, they then have to be brought back very slowly toward the material still located in the cartridges in order to carefully make contact with the material still present therein. The retraction movement could also have the undesired effect of allowing air into the cartridges.